update docker build commands in Makefiles to use buildx (#3137)

* switch to docker buildx and update docs
* minor update to e2e Dockerfile

charts/postgres-operator/crds/postgresqls.yaml

@@ -457,6 +457,7 @@ spec:
               envFrom:
                 items:
                   description: EnvFromSource represents the source of a set of ConfigMaps
+                    or Secrets
                   properties:
                     configMapRef:
                       description: The ConfigMap to select from
@@ -476,8 +477,9 @@ spec:
                       type: object
                       x-kubernetes-map-type: atomic
                     prefix:
-                      description: An optional identifier to prepend to each key in
-                        the ConfigMap. Must be a C_IDENTIFIER.
+                      description: |-
+                        Optional text to prepend to the name of each environment variable.
+                        May consist of any printable ASCII characters except '='.
                       type: string
                     secretRef:
                       description: The Secret to select from
@@ -498,7 +500,6 @@ spec:
                       x-kubernetes-map-type: atomic
                   type: object
                 type: array
-                x-kubernetes-list-type: atomic
               initContainers:
                 items:
                   description: A single application container that you want to run